End of Community season 2. The whole season built to the showdown of Pierce vs the group, with everyone but Annie voting to kick him out, and then he surprised everyone by saving the school and then voluntarily leaving the group. Season 3 should have been the story of Pierce away from the group, and how they realized that they needed him (and he needed them).

Instead, he was back in the group right from the intro to Season 3 with nary a mention of what had happened, and with the group again trying to get rid of him. It felt like the entire payoff of the season 2 finale was just for naught.